20 30 40 



, ANGLE FROM VERTICAL, deg 



DIRECT PATH 



MULTIPATH 



Figure 12. Signal to multipath ratio as a function of angle from the vertical. 

 4. CONCLUSION 



The FY 77 SUBSAT experiments presented herein have shown the feasibility of trans- 

 mitting 7200-baud acoustic slow-scan television using off-the-shelf equipment to generate and 

 receive the slow-scan video in conjunction with existing UQC gear. The cost of the slow- 

 scan equipment was approximately $ 1000 per transmitting or receiving installation. Equip- 

 ment installation can be accomplished within an hour by simple cable interconnection. No 

 modification of the UQC is necessary nor is its usual voice function disabled. In 26 separate 

 acoustic video transmissions during the SEACLIFF and DOLPHIN tests no hardware failures 

 were encountered. 



All of the acoustic video transmitted from depth was received on the surface; received 

 in the sense that from the marking of the video monitor it was clear that a video trans- 

 mission was occurring. However, most of the received transmissions were noticeably degraded 

 compared to the transmitted picture quality, the most persistent problems being line sync 

 failures and granulation. Evidence gathered during the experiments suggests that the observed 

 image degradations were due to a low signal-to-multipath ratio, which in turn was caused by 

 a large horizontal offset between sending and receiving platforms. 



The FY 1978 SUBSAT program, already underway, will be directed at obtaining 

 additional data under more carefully controlled conditions. In particular it will attempt to 

 show what is currently predicted from the FY 1977 experiments: that useful acoustic slow- 

 scan imagery can be transmitted reliably, provided that undue horizontal offsets between 

 sending and receiving platforms can be avoided. Such a demonstration would validate the 

 SUBSAT hardware approach and indicate that a video imagery capability can be added to 

 existing UQCs at modest cost by using off-the-shelf units. 



20 



